Lead
Lead is a main-group element with symbol Pb and atomic number 82. Lead is a soft, malleable poor metal, also considered to be one of the heavy metals. Lead has a bluish-white color when freshly cut, but tarnishes to a dull greyish color when exposed to air. It has a shiny chrome-silver luster when melted into a liquid.Lead is used in building construction, lead-acid batteries, bullets and shot, weights, and is part of solder, pewter, fusible alloys and radiation shields. Lead has the highest atomic number of all stable elements, although the next element, bismuth, has a half-life so long (longer than the estimated age of the universe) it can be considered stable. Lead is a poisonous metal that can damage nervous connections (especially in young children) and cause blood and brain disorders. Like mercury, another heavy metal, lead is a potent neurotoxin that accumulates in soft tissues and bone over time. Lead poisoning was documented in ancient Rome, ancient Greece, and ancient China. Characteristics Lead is a dense, ductile, very soft, highly malleable, bluish-white metal that has poor electrical conductivity. This true metal is highly resistant to corrosion, and because of this property, it is used to contain corrosive liquids (e.g., sulphuric acid). Because lead is very malleable and resistant to corrosion it is extensively used in building construction, e.g., external coverings of roofing joints. Lead can be toughened by addition of a small amount of antimony or other metals. All lead, except 204Pb, is the end product of a complex radioactive decay. Lead is also poisonous, as are its compounds. Lead has many isotopes but 4 stable ones. The 4 stable isotopes are 204Pb, 206Pb, 207Pb and 208Pb with 204Pb regarded as primordial lead and 206, 207, 208 are formed from decay of uranium and thorium. The one common radiogenic isotope, 202Pb, has a half-life of approximately 53,000 years. Various oxidized forms of lead are easily reduced to the metal. An example is heating PbO with mild organic reducing agents such as glucose. A mixture of the oxide and the sulphide heated together will also form the metal. Metallic lead is attacked only superficially by air, forming a thin layer of oxide that protects it from further oxidation. The metal is not attacked by sulphuric or hydrochloric acids. It does; however, dissolve in nitric acid with the evolution of nitric oxide gas to form dissolved Pb(NO3)2. When heated with nitrates of alkali metals, metallic lead oxidizes to form PbO (also known as litharge), leaving the corresponding alkali nitrite. PbO is representative of lead's +2 oxidation state. It is soluble in nitric and acetic acids, from which solutions it is possible to precipitate halide, sulphate, chromate, carbonate (PbCO3), and basic carbonate (Pb3(OH)2(CO3)2) salts of lead. The sulphide can also be precipitated from acetate solutions. These salts are all poorly soluble in water. Among the halides, the iodide is less soluble than the bromide, which, in turn, is less soluble than the chloride. Lead(II) oxide is also soluble in alkali hydroxide solutions to form the corresponding plumbite salt.Chlorination of plumbite solutions causes the formation of lead's +4 oxidation state. Lead dioxide is representative of the +4 oxidation state, and is a powerful oxidizing agent. The chloride of this oxidation state is formed only with difficulty and decomposes readily into lead(II) chloride and gas. The bromide and iodide of lead(IV) are not known to exist. Lead also has an oxide with mixed +2 and +4 oxidation states, red lead (Pb3O4), also known as minium.Lead readily forms an equimolar alloy with sodium metal that reacts with alkyl halides to form organometallic compounds of lead such as tetraethyl lead. Value The base value of each unit of ranges between 1 and 15Ð per unit, with up to 3 units being found at any one time. Presence on Mars: Rare Category:Chemical elements